Like function templating using the Function constructor, try-catch wrapping, closure avoidance and many more. The source is a goldmine of JS optimization techniques (some V8-specific, some not so much)
This sounds very interesting even to those of us who don't need a promises library. If you or anyone else would like to go into detail, I bet a lot of people here would care (including me).
esailija is the author, and I believe he mentioned that he is planning to write an optimization guide (specific to the library, though it will probably contain generally useful info).
